With the recent advances in the reduction in size and the increase in capacity of magnetic disk drives, there is a need to increase the recording density. To increase the recording density, techniques for further reducing the flying height of magnetic heads are being developed so as to decrease the unit recording area and improve the detection sensitivity for a weakened magnetic signal. In order to take measures for reducing the flying height of magnetic heads and securing the recording area, the requirements for magnetic disk substrates are becoming increasingly stringent, with regard to the improvement of smoothness and flatness (the reduction of surface roughness, waviness, and roll-off) and the reduction of defects (the reduction of scratches, protrusions, pits and the like). To satisfy such requirements, polishing compositions containing a copolymer having a functional group such as a carboxyl group and a sulfonic acid group have been suggested (for example, see Patent Documents 1 to 3).
Patent Document 1 discloses a polishing composition suitable for chemical mechanical polishing (CMP) of semiconductor components. This polishing composition contains a polymer having a sulfonic acid group, and thus makes it possible to planarize the surface of an object to be polished, and also increase the polishing rate.
Patent Document 2 discloses a polishing composition for semiconductor components that is suitable for chemical mechanical polishing (CMP). This polishing composition contains at least two polymers selected from a polymer having a carboxylic acid group, a polymer having a sulfonic acid group, and a polymer having a phosphoric acid group, and thus makes it possible to reduce the surface roughness of an object to be polished, and also increase the polishing rate.
Patent Document 3 discloses a polishing composition for Ni metal-containing substrates. The polishing composition contains particles of a copolymeric resin having a functional group, such as a sulfonic acid group, capable of coordinating with a metal ion, instead of inorganic abrasive grains such as alumina and silica, and thus can suppress the occurrence of defects such as scratches and protrusions.